Method for the treatment of wood, wood powder and such, equipment for the treatment of wood, products made from the modified wood and products made from the treated wood powder and such

ABSTRACT

The invention relates to a method, for the treatment of wood. wood powder and like through waiting with an aqueous solution, which contains one or more bifluorider. The invention relates further to the improvement of the drying of “green” wood and not completely dry wood. The invention relates to a method for the method of wood, an equipment for the realization thereof, a method for the treatment of wood powder like, wooden products consisting of treated wood powder.

The invention relates to a method for treatment of wood by means ofwetting of the wood, wood powder and so with an aqueous solutioncontaining one or more bifluorides and to products made from the treatedwood itself and to products consisting of the treated wood powder.

With respect to the previous, from Dutch Patent No. 1004556 a method isknown for the treatment of wood, by which the bifluoride solutioncontains 8-32 weights % of both potassium and ammonium bifluoride in aweights proportion of the potassium to the ammonium salt between 13:7and 2:3. The treatment known from Dutch Patent No. 1004556 has aspurpose the improvement of the moisture regulating properties of thewood or the products made from that.

A problem with green wood is that it cracks by drying too fast, with theresult that per unity of volume less useful products can be made fromthat.

From John H. Perry, Chemical Engineer's Handbook, Second Edition, McGrawHill Book Company, New York, p. 1509, for the solution of this problem alumber dryer is known, by which wood is dried at elevated temperatureunder controlled relative humidity with heated air.

The said dryer is called “Tiemann lumber dryer” and a cross-section ofthis dryer is shown as FIG. 9 on p. 1509 of the previously mentionedpublication.

Self-evidently drying with heated air under controlled relative humidityis quite expensive, more especially because of the heat needed.

From JP-A-07-314409 (Chem. Abs. 124:149094v) another method forimpregnation of wood without the necessity of pre-drying, by whichcracking of the wood is prevented, is known.

First the “green” wood is impregnated with an organic solvent,compatible with wood and miscible with water. After extraction andreplacement of most of the water with organic solvent, subsequently thewood is impregnated with preserving agents soluble in the organicsolvent

Self-evidently this impregnation is expensive and it can be questionedwhether the organic impregnation agents used are sufficiently harmlessfor the environment.

The present invention intends in the first place to improve in anefficient way the moisture regulation of wood, more especially greenwood (which thus contains quite an amount of water).

According to the invention the wood is immersed or sprayed on all sidesduring at least 3 minutes with the bifluoride solution.

With the treatment according to the invention one is not limited to themixture of potassium and ammonium bifluoride of Dutch Patent No.1004556, but eventually other bifluorides with a high solubility inwater could be used too.

Discovered was namely that during the very short all sided wetting ofthe wood, the bifluoride penetrates sufficiently deep in the outerlayers of the wood for improving the drying process in such an extent,that heated drying with risk of cracking becomes superfluous.

In this case the wetting of the wood has to be all sided

During a wetting of the wood, the bifluoride Ion (FHF′) from the mixedbifluoride solution penetrates very quickly in the outer layers of thewood.

As before mentioned, the invention is based on the discovery that whenthe amount of water capacity is greater than the amount of water presentin completely dry wood, the chemisorption of FHF′ on cellulose is as ifit were catalysed and therewith enters in a lasting bond with cellulose.

According to the invention one can use also in addition to the mixtureof potassium and ammonium fluoride mentioned in Dutch Patent No. 1004556another alkali bifluoride, and one can use the bifluorides separatelyalso, provided that with wood is satisfied on the concentration of 8-32weights %.

A preferred wetting solution is the solution mentioned in Dutch PatentNo. 1004556 of potassium and ammonium bifluoride by which the weightsproportion between both bifluorides is between 13:7 and 2:3.

In addition to the before mentioned alkali bifluorides, it is possiblealso to use one or more other bifluorides, which are fairly soluble,zinc bifluoride for instance is conceivable.

Self-evidently the wetting solution may contain other soluble metalsalts in addition to one or more alkali bifluorides and/or zincbifluoride.

Arbitrarily in the sense of thine invention it can be postulated thatgreen wood or incompletely dry wood is wood with a moisture contentabove 8 weigts %.

As consequence of the treatment through all sided wetting withbifluoride solution according to the invention, the moisture content inthe outer layers of the wood increases during a short time with severalpercents. During drying the moisture content in the outer layers of thetreated wood falls rather quickly to somewhat below the initial moisturecontent preceding the immersion treatment.

The consequence of the wood treatment is that the outer layers withchemisorbed bifluoride dry better with conservation of the moistureregulation properties of the wood.

Preferably the all sided wetting can take place trough immersion onlath.

It is noted that in Dutch Patent No. 10045S6 on p. 5 lines 26 and 27 Itis mentioned that if necessary wooden components eventually can alreadybe placed on lath during the immersion in the solution of the combinedbifluorides.

However components are wooden parts, which as a rule are made from woodpre-dried in the wood producing countries.

The method according to the invention now can advantageously be appliedon “green” wood or incompletely dry wood.

As mentioned before, it has been discovered that amounts of watergreater than me equilibrium concentration in dry wood accelerate greatlythe penetration of the FHF′.

With “green” wood are meant tree-trunks of just felled trees, whether ornot stripped of their bark or boards or beams sawed there from a shorttime after felling.

Self-evidently this has great consequences for the wood industry, woodcan now namely almost simultaneously be treated wit bifluoride solutionand dried.

The method according to the invention can advantageously be applied asfollows.

One uses a bifluoride solution with a weights concentration between 8and 16 weights % for wood with a moisture content between 10 and 35%;for more humid wood one uses a bifluoride solution with a higher weightsconcentration. Therefore a bifluoride solution with a weightsconcentration between 15 and 32 weights % is used for wood with amoisture content between 35 and 60%.

According to a preferred method and equipment, with which green wood orincompletely dry wood can be treated, is wood as with the known quickdry installation stacked in such a way on transport vehicles, that warmdrying air can flow through and along the tree-trunks to be dried, oneelaborates more or less on the here before mentioned “Tiemann's lumberdryer”.

With the method and equipment according to the invention, the wood isfirst stacked on lath in a transport container.

The equipment includes in addition to the transport container animmersion vessel with agitation means for improvement of the all sidedrinsing of the wood with the bifluoride solution and means for bringingin—and out—of the transport container in the immersion vessel.

After immersion of the wood in the immersion vessel, the wood is liftedout of the bifluoride bath and is left over to draining in the immersionvessel.

After draining the wood is ready for transport in the transportcontainer and dries due to the improved moisture regulating propertiesalready during the transport,

The immersion vessel is hereby provided with dosing means for bifluoridesolution.

The invention relates also, as mentioned in the preamble of thedescription, to a method for obtaining pre-treated wood powder, woodpulp, or other desintegrated products from materials with a highcellulose content, such as textile, by treatment with the bifluoridesolution.

The product obtained by means of the pre-treatment is through thatbetter suited for manufacture of formed objects or the formed objectspossess better properties.

The invention relates also to objects obtained out of the pre-treatedproduct or which consist partially thereof.

In relation to the foregoing, from JP-A-07-178727 (Chem. Abs. 123:202600q) a cellulose powder is known, obtained from wood, bagasse orstraw, which is sprayed with an anti-bacterial agent and used as fillingagent for plastic mouldings (such as panels) and as coatings.

The invention now relates also to improvement of the moisture regulatingproperties of cellulose treated with bifluoride and/or formed objectsthereof.

With treated cellulose in the sense of the invention is meant also woodpulp, cotton linters, flax fluffy and like materials, whether or notgrinded straw or bagasse.

The thought of the invention to expand the invention to wood powder andsuch, elaborates model experiments performed in order to imitate theeffect of relatively small amounts of bifluoride on the good moistureregulation of wood treated with potassium and ammonium bifluoride and tofind out the probably cause thereof.

Most probable the improvement of the properties is due to chemisorptionof FHF′ ions on cellulose, whereon follows complete modification.

Continuing with the obtained improved properties of the treatedcellulose, it is now proposed to pre-treat with bifluoride wood powderand possibly other fairly fine products, such as cotton linters and flaxfluffy after which it is the intention to convert the treated materialfurther to useful products.

Other fairly fine products are straw, broken flax stalks and cottonfiber.

The invention relates also to wood modified with bifluoride solution orwooden products made thereof.

As mentioned before the invention relates in principle to improvement ofthe properties of cellulose treated with bifluoride and/or formedobjects hereof.

With treated cellulose in the meaning of the invention is meant alsowood powder, cotton linters, flax fluffy and like materials such aswhether or not grinded straw or bagasse.

The invention elaborates on model experiments performed as a result ofDutch Patent No. 1004556 in order to imitate the effect of relativelysmall amounts of bifluoride on the good moisture regulation of a woodtreated with potassium and ammonium bifluoride and to find out theprobably cause thereof.

Most probably the improvement of the properties is due to chemisorptionof FHF′ ions on cellulose.

In addition to modified wood and products manufactured there from, theinvention relates also to products manufactured from the treated woodpowder and like.

The invention is illustrated now with four examples and a graph withrespect to the penetration depth in wood, and a graph with respect tothe moisture regulation behaviour of treated cellulose.

With respect to the examples and the graph of the penetration in wood itis firstly remarked that the moisture content of wood is determined withthe formulaA_(x−B×)100%, wherein

-   -   A₁₀₀    -   A_(x) weight of wood with a certain moisture content    -   A₁₀₀ weight of wood which is completely moist,    -   B weight of wood which is completely dry.

The weight of completely dry wood is determined through drying thisduring 24 hours at 110° C.

Ax is the weight of wood with a moisture content between 0 and 100%.

Further it is remarked with respect to the penetration depth ofbifluorides in wood that this is determined with zirconyl-allzarine Sreagent (J. H. de Boer, Chemisch Weekbiad 21, 404 (1924)).

Firstly the wood treated with bifluoride solution is sawed offtransversely to the penetration depth and subsequently thinly sprayedwith zirconyl-allzarine S reagent. On the spot, or penetration depth,where chemisorbed bifluoride is present, this reacts with the red-violetzirconyl-allzarine S. By the reaction with the bifluoride, thered-violet colour is changed in pale yellow (that of the liberatedallzarine sulfonic acid) because of the formation of the colourlessbivalent zirconium hexafluoride Ion ZrF_(a)″.

With respect to the penetration depth in wood of a bifluoride solutionfollow first below four examples with two different concentrations ofthe bifluoride solution and two different humidities of the wood.

The immersion times of the wood were in all cases 10 minutes.

EXAMPLE 1

Concentration bifluoride solution:

-   -   Humidity of the wood 13%    -   Penetration 12 mm

EXAMPLE 2

Concentration bifluoride solution:

-   -   Humidity of the wood 60%    -   Penetration 40 mm

EXAMPLE 3

Concentration of the bifluoride solution:

-   -   Humidity of the wood 13%    -   Penetration 18 mm

EXAMPLE 4

Concentration of the bifluoride solution:

-   -   Humidity of the wood 60%    -   Penetration 70 mm

In the accompanying figures is FIG. 1 a graph, which indicates withequal immersion times (10 minutes) of wood with different humidities therelation between the penetration depth of the bifluoride solution andwood humidity for different concentrations of a bifluoride solution.

FIG. 2 is a graph, which indicates the moisture regulation behaviour ofcellulose treated with different concentrations of bifluoride andcellulose treated with demineralised water only.

FIG. 1 shows, as mentioned above, the relation between penetration depthof a bifluoride solution and the wood humidity.

Along the X-axis is represented the wood humidity in percents, startingwith 8.0%, which represents the percentage at heating of the wood during24 hours at 110° C.

Along the Y-axis is represented the penetration depth determined withzirconyl-allzarine S as mentioned before. The penetration depth isindicated in cm.

In the graph of FIG. 1 are represented with respectively 1, 2, 3, 4, 5and 6 the curves with concentrations of 17, 15, 13, 11, 10 and 8.5%.

FIG. 2 relates as mentioned before to the moisture regulating behaviourof cellulose respectively treated with a 10% mied bduodde solution anddemineralised water.

As cellulose is the most important constituent of wood, the followingexperiments with cellulose were performed in order to demonstrate thechanges in adsorption behaviour of wood.

With the experiments with cellulose six A4 sheets bleached softwoodcellulose pulp were respectively immersed in bifluoride solution anddemineralised water, each three pieces.

The cellulose pulp sheets weighted each about 50 grams.

The 10 seconds immersion time is beforehand determined as the maximalimmersion time before the specimen disintegrates through the action ofmoisture.

After immersion the specimen was dried at the air during 1 minute andsubsequently fastened on a weighing device in a climatic room.Subsequently, the cellulose sheet was equilibrated with the environmentduring 8 hours, at 23° C. at 50% RH (relative humidity) before startingthe experiment

With the three experiments of cellulose treated with bifluoride and thethree experiments treated with demineralised water, the cellulose sheetwas first exposed to an air atmosphere of 23° C. with a RH of 85% duringabout 8 hours and subsequently to an air atmosphere of 23° C. with a RHof 35% during about 7 hours.

Along the Y-axis now the weight of the six test sheets is indicated ingrams, the X-axis indicates the time in respectively hours, minutes andseconds.

The weights of all the six specimens at the start of the individualexperiments are about 50 grams, the weights of the three cellulosesheets treated with bifluoride gradually increase with about 8 grams ofwater, at lowering of the RH to 35%, the absorbed water rather steeplydisappears except to about 2 grams.

With a cellulose sheet treated with demineralised water only, the weightincreases much less than with a specimen pre-treated with bifluoride.Herewith the increase in weight is about 1.5 grams only and returns withRH reduction much less steeply to about the weight at the start of theexperiment.

In FIG. 2, in which the test results of six different experiments areindicated, the three different experiments with bifluoride arerespectively indicated as BF1, BF2 and BF3.

The experiments with demineralised water are respectively indicated asDW1, DW2 and DW3.

It is noted that in FIG. 2 the curves of the water absorption anddesorption in a certain way lie above those of the specimens treatedwith demineralised water

Prolonged experience with wood treated with bifluoride solution hasshown that this through the changed water absorbtion behaviour, which issupported by the fast absorption and desorption of water with change ofRH of cellulose, has improved properties with respect to wood moistureregulation.

The moisture absorption behaviour of wood changed through the treatmentwith bifluoride solution extends also to wood powder, wood pulp or otherdisintegrated products from materials with a high cellulose content.

In addition to the above mentioned concept of the improved moistureregulation of wood or disintegrated cellulose containing materials, theinvention relates as mentioned before to the discovery that thepenetration of aqueous bifluoride solution is if it were catalysed bymoisture.

Because of this the advantage originates that one has not to impregnateunder pressure or vacuum a wood preservation solution in order to obtaina sufficient penetration depth.

1. Method for the treatment of wood, wood powder and the like, bywetting with an aqueous solution of one or more bifluorides,characterized in that, more especially for the purpose of drying, oneimmerses or sprays the wood or the wood powder and the like during atleast 3 minutes.
 2. Method according to claim 1, characterized in that,one immerses the wood on lath.
 3. Method according to claim 1,characterized in that, one sprays the wood all sided.
 4. Methodaccording to claim 1, characterized in that, one uses for the wetting anaqueous solution which contains one or more alkali bifluorides. 5.Method according to claim 4, characterized in that, the bifluoridesolution contains potassium and ammonium bifluoride, in which theweights ratio between both bifluorides is between 13:7 and 2:3. 6.Method according to claim 1, characterized in that, the bifluoridesolution contains one or more other bifluorides as for instance zincbifluoride, and if necessary other soluble metal salts.
 7. Methodaccording to claim 1, characterized in that, one applies the method ongrenn wood or incompletely dry wood.
 8. Method according to claim 7,characterized in that, one applies a mixed bifluoride solution with aweights concentration between 8 and 15 weights % with wood with amoisture content between 10 and 35% and a mixed bifluoride solution witha weights concentration between 15 and 32 weights % with wood with amoisture content between 35 and 60%.
 9. Method according to claim 1,wherein airily stacked wood is placed on a transport container, andsubsequently immersed on all sides in aqueous bifluoride solution andafter draining, if desired dried and transported.
 10. Equipment forperforming the method according to anyone of claims 1, 2, 3, 4, 5, 6, 7,8 or 9, comprising a transport container for wood, wherein wood can beairily stacked, characterized in that, the equipment further comprisesan immersion vessel wherein fits the immersion vessel provided withagitating means arid transporting means for bringing in and bringing outof the transport container and dosing means for supply of bifluoridesolution.
 11. Modified wood or wooden products produced according to themethod of any one claims 1, 2, 3, 4, 5, 6, 7, 8 or 9, characterized inthat, this contains in the outer layers about 15% moisture.
 12. Productsmanufactured from wood powder and the like treated with bifluoridesolution according to the method of any one of claims 1, 2, 3, 4, 5, 6,7, 8 or 9.